Wow, I don't even understand half the stuff you said. There's so much to singing.
In oversimplified terms, your modal voice is your usual singing/speaking voice, and your falsetto voice is the one above it which you use for making fun of opera singers and teasing friends. In a physical sense, the modal voice vibrates your entire vocal cord, while the falsetto holds most of it still and uses only the outer and upper edge.
* You also have two additional registers. Below modal is vocal fry, which is deep in the throat and sort of "bubbles" air through the cords like a croak. Above falsetto is whistle, which is the really annoying shit babies can scream when they hate your soul — the physical mechanism isn't entirely understood since the epiglottis closes and we can't see it with cameras like we can the others.
To see this in action, hum a low note and then drag it upwards as high as you can. There'll be a quick airy pause as you naturally transition to falsetto — this is your vocal break.
The ranges of each depend on your personal characteristics (size of the cords etc) and how well you've developed it, and the break will vary. Typically, the modal and falsetto ranges overlap somewhat by an octave or so, but they have different tone quality because they use your vocal cords in completely different ways. Generally, you want to keep from switching between them in the middle of a musical phrase — not only for the sake of sounding consistent across the phrase, but also because moving between them tends to have that brief, airy break while your vocal cords go "oh shit I have to do this other thing!" and change vibration modes.
This Day has the singer use the modal voice for Chrysalis and the falsetto for Cadence to distinguish their voices — notice Cadence sounds more airy, while Chrysalis sounds more dark and solid even though for their intros they're singing the same notes. But Chrysalis's prima donna moment in the middle pushes the upper bound of modal voice. That limit is dictated by how easily you can move the entire vocal cord instead of just the upper edge, so you can extend its range a bit by just pushing air harder (which this song allows there by getting louder there) and being very careful to keep the throat relaxed, but it's exceedingly difficult to control and you can go out of tune really fast. Likewise, most of Cadence's part pushes the lower edge of falsetto, but pulling that off is less risky.
Looking back on the English version, it sounds like the original singer just went ahead and jumped to falsetto for that couple of measures (where the camera pitches up to the chandelier and spins) instead of trying to power through it like the German one tried, but she masked it really,
really well.
tl;dr, from a technical standpoint that song is more of a nightmare than it sounds.
edited 8th Oct '12 5:30:49 PM by Pykrete